NOTA PALEONTOLOGICA ASTRAPOTHERIUM Sp. (MAMMALlA, ASTRAPOTHERIIOAE) FROM MIOCENE STRATA ALONG THE QUEPUCA RIVER, CENTRAL CHILE LARRY G. MARSHALL Institute 01 Human Origins, 2453 Ridge Road, Berkeley, California 94709, U.S.A. PATRICIA SALINAS Museo Nacional de Historia Natural, Sección Geologla, Casilla 787, Santiago, Chile MANUEL SUAREZ Servicio Nacional de Geologra y Mineda, Casilla 10465, Santiago, Chile ABSTRACT The teeth of a single individual of a large extinct mammal, Astrapotherium sp. (Astrapotheriidae), were recently recovered from Tertiary sediments correlated to the Cura-Malllín Fomation exposed along the Quepuca River, Biobío Region, Central Chile. Although the species has yet to be securely determined, the remains are comparable with Astrapotherium magnum (Owen, 1853) and A. hesperinum Cabrera, 1940, from racks of Santacnucian Mammal age (late Early Miocene) in southern Argentina and Chile. It is therefore postulated that at least part of the host rock unit containing these fossils i - of that age. The rocks containing the fossil teeth of Astrapotherium sp. were apparently deposITed in a meandering stream and flood plain environment. The presence of this vertebrate fossil also suggests abundant vegetation in !he area. Key words: Astrapotherium, Santacrucian Land Mammal Age, Cura·Mal/En Formation, REo Pedregoso strata, Miocene, Chile. RESUMEN Recientemente, fueron recolectadas piezas dentarias de Astrapotherium sp. (Astrapotheriidae) en estratos terciarios, correlacionables con la Formación Cura-Mallín, expuestos a orillas del río Quepuca, en la Región del Biobío, Chile Central. Si bien no ha sido posible alcanzar una identificación especifica, los restos son comparados con Astrapotherium magnum (Owen, 1853) y A. hesperinum Cabrera, 1940, formas características de Edad-mamífero Santacrucense (Mioceno Inferior tardlo) del sur de Argentina y Chile. Se postula, en consecuencia, que al menos parte de la formación que contenía estos fósiles tiene esa edad. Las rocas en las cuales se recolectaron las piezas dentarias deAstrapotherium sp., fueron depositadas, aparentemente, en un ambiente de río meandriforme y de planicie de inundación; el vertebrado fósil sugiere también la presencia de abundante vegetación en el área. Palabras claves: Astrapotherium, Edad MamEfero Santacrucense, Formación Cura-Mallfn, Estratos de REo Pedregoso, Mioceno, Chile. INTRODUCTlON On February 24, 1989, the upper molar of an ex­ from the Servicio Nacional de Geología y Mineda, tinct mammal attributed to Astrapotherium (Astrap­ and the authors visited this locality on Novem:>er 18, otheria, Astrapotheriidae) was collected by Nicolás 1989, and recovered the upper right P4-M3 of the Blanco, a Geology student at the Universidad de same animal. This is the first record of Astrapothe­ Concepción, and one of the authors (M.S.) from Ter­ rium for the Tertiary sedimentary rocks exposed tiary sedimentary rocks along the east bank of the north of the Aisén Region, and it is of special impor­ Quepuca River, a tributary of the Biobío River, in tance for delimiting the age of the host strata (equi­ Central Chile (38°0,29'S; 71°24,3'W, Text-Fig. 1, for valent to the Cura-Mallín Formation of Nieme~'er and geographicdata see Sheet Curacautín, SJ-19-9 3800- Muñoz, 1983). 7030, scale 1 :250.000,lnstituto Geográfico Militar, In this note the authors give a preliminary identi­ 1985). Afterwards, Carlos Emparan, Renate Wall, fication of this fossil, place it in stratigraphic context, Revista Geológica de Chile, Vol. 17. No. 2. p. 215·223, 3 Figs.• 1 Lám. ASTRAPOTHERlUM sp., MIOCENE, CENTRAL CHILE 216 19° 32° Base topogrófico: Reducción de ,corto reQulor Lolco, escola 1:50.000 I.G.M. 2 km o Localidad fosilífera Text-Fig. 1. Map showing locality where Astrapotherium sp. was collected. and discuss its age implications for the rock unit found in rocks of Oligocene-Miocene age (Mones, which contains it. 1986). The only previous reports of Astrapotherium Bur­ Abbreviations include: L. length; W. width; m: meister, 1879, forChile are aspecimen of A. magnum meters; cm. centimeter; mm. millimeters; M. upper from the Palomares (=Santa Cruz) Formation at molar; Ma. megaannum or millions of years ago, a Laguna del Toro in Magallanes (Hemmer, 1935) and point in time; MNHN SGO-PV: Museo Nacional de the type of A. hesperinum from the Río Frías Forma­ Historia Natural, Santiago, Sección Geología, Verte­ tion in Aisén (Cabrera, 1940). In South America, brate Paleontology collections. genus Astrapotherium is represented by 23 species STRATIGRAPHIC CONTEXT Widespread volcano-sedimentary successions and equivalent to the Malla-Malla Member of the of Tertiary age, assigned to the Cura-Mallín Forma­ Cura-Mallín Formation of Niemeyer and Muñoz, tion (sensu Niemeyer and Muñoz, 1983) and its 1983), and composed of sandstones, shales, ash-fall equivalent units (>1.000 m thick; Suárez and Em­ tuffs and tuffites, conglomerates, volcanic debris paran, 1988; in prep.), crop out in the Andean region flows, lahars, subordinate pyroclasticflows, oil-shales, between latitudes 38° and 39°S. They comprise limestones and lava flows, deposited in lacustrine, three main units, which from an older to younger stra­ deltaic and fluvial systems; and c. a uni! of orthocon­ tigraphic order (however b. overlies and late rally in­ glomerates, debris flow deposits and ignimbrites, terfingers with a.) are: a. a mainly volcanic complex, deposited by alluvial systems and typically exposed well exposed in the Guapitrio River (equivalent to the in the Tralilhue and Liucura rivers. Río Queuco Member of the Cura-Mallín Formation of An Eocene-Miocene age range for the sedimen­ Niemeyer and Muñoz, 1983), formed principally by tary strata exposed in the Pedregoso River has been ash-fal.ltuffs, pyroclasticflows, lava flows, and tuffites suggested by previous authors (i.e. Osorio et al., and sandstones of a lacustrine and fluvial facies; b. 1982; Palma-Heldt, 1983; Cisternas and Díaz, 1985). a main ly sedimentary unit well exposed in the Pedre­ An important lacustrine facies association included in goso River (Río Pedregoso Beds of Sandoval, 1977, these strata developed between 17.5 ± 0.6 (biotite) L.G. Marshall, P. Salinas y M. Suárez 217 and 13.0 ± 1.6 Ma (whole rock), as indicated by K-Ar Ma (Suárez and Emparan, 1988). dates on an intercalated tuff and lava Il0w, respec­ The Astrapotherium 10ssil remains were collect­ tively (Suárez and Emparan, 1988; in prep.). ed lrom the upper part 01 a 14 m exposure 01 cross­ Radioisotopic (K-Ar) dates indicate that these bedded sandstones and shales exposed along the rocks accumulated between 22.0±O,9 and 10.7± 1.1 Quepuca River (Text-Figs. 1,2), and comparable to some 01 the fluvial and lacustrine facies exposed Blacklhal•• along the Guapitrio River, about 25 km to the south (Text- Figs. 1, 2). The measured section includes, Volcanicsandstona. w~h &Canered pebble.: from top to bottom: a. cross-badded b. poorly expeled. no Intarnal structures can be racognlzad 4.00 m Coset of cross-bedded light-green volcanic sandstones, with scattered pebbles (Iess than 1 cm in diameter). Tun., probably . I ~." 4.00 m Dark gray massive shales occasionally lami­ nated; with medium-grained sand grains and slickenside planes common; the teeth of Astra­ potherium were collected in upper 0.5 m; no other fossil vertebrates were observed. 0.65 m Fine to medium-grained light green volcanic sandstones (badly exposed). 1.00 m Dark gray shales with scaltered fine to medium­ grained sands; slickenside planes common . 1.80 m Coset of cross-bedded light green volcanic sand­ stones; fine to medium-grained with isolated pebbles; no upward grain size variation observed; sorne slickenside planes. 5 0.30 m Dark gray shales, massive, with medium size­ Text-Fig. 2. Stratigraphic section of grained sand clasts. beds along the Quepuca 0.10 m Tuff; poorly exposed (airfall?). River, showing lithology and level where fossil 0.20 m Dark gray sandy shale; probably faulted upper was collected. Faulting in contact. the shale horizons (not 1.30 m Light green medium-grained volcanic sand­ shown in the figure) may stones. have altered the column. 0.25 m Greenish-gray tuffaceous shale, fissile, with car­ bonaceous seams and slickenside planes. 0.30 m Massive medium gray tuff. '"O Unexposed base FOSSIL Thefossil material includes an isolated left upper Although the right P4-M2 were found together, there third molar (M3) (Text - Fig. 3a-c) and right upper is no trace 01 the maxillary bone nor were any bone fourth premolar (P4) and three molars (M1-3) (PI. 1, fragments observed. Figs. 1-3). The right P4-M2 were recovered in sequen­ The fossil is conlidently referable to the genus tial contact, while the left and right M3's were isolated. Astrapotherium (order Astrapotheria, family Astrapo­ AII 01 the teeth were 10und within 1 mol each other, theriidae) which is known only from Early Miocene in situ, and in the same level. Based on similarities 01 rocks 01 Colhuehuapian and Santacrucian age in occlusal wear the authors believe that they are all Argentina and Chile (Bondesio. 1986; Marshall et al., referable to a single individual (MNHN SGO-PV 4003). 1986; Marshall and Salinas, 1990). However, the Except 10r minor damage to the posterior edge 01 identity of the species is uncertain. This is due to the the right M2 and medio-labial edge of the right M3, the fact that 23 species names have been assigned to teeth are complete and remarkably well preserved. Astrapotherium (see Mones, 1986, p. 180) and these 218 ASTRAPOTHERIUM sp., MIOCENE, CENTRAL CHILE Texl-=ig. 3. Astrapotherium sp. (Aslrapolheria, Aslrapolheriidae) from slrala exposed along Quepuca River. MNHN SGO-PV 4003. Left M3, s.labial; b. occlusal; e.lingual views. Measuremenls (in mm): M3 L = 58.4, W = 45.3. have not received a synthetic systematic revision. solely on size, recognized three Santacrueian spe­ Consequently, the number of valid species has yet to eies as valid: A.